The present invention relates to a covering sheet, a triplate line using the sheet, a signal bus for a computer using the sheet, and a covering structure of an electronic circuit using the sheet. Particularly, the present invention relates to a technology for achieving higher pbu of a signal bus mainly for a computer and to an electromagnetic-interference-preventing technology for suppressing unwanted signal radiation observed in signal lines of electronic equipment.
Generally, the speeding up of central processing units (CPUs) has been pursued in order to increase the clock frequency of computers. However, there is a limit to what is done by increasing the speed of only CPU""s, the achievement of the further increased processing-speed of computers requires the increased speed of data exchange between CPU""s and peripheral equipment.
As shown in FIG. 1, a CPU 10 and peripheral equipment 11 to 14 are usually connected to each other through lines having a plurality of branches and being called a signal bus 15. The signal bus 15 should be made of non-matched branch lines, because talkers (sending ends) and listeners (receiving ends) change places as required. As a result, there can be troubles such as the delay of pulse build up (pbu) time, caused by the irregularities of pulse shapes resulting from the existence of reflected waves in the lines, and the break down of semiconductor elements due to voltage buildups caused by resonance.
In order to avoid such troubles, conventionally, damping resistance and absorbing type of high-cut filters have been inserted into the circuits. However, these measures have not been sufficient, because they have respective problems that pbu time can not be appreciably reduced and that not only signal waveforms but also the lengths of delay time are different before and after the filter.
On the other hand, there have been the following problems in the electromagnetic control technologies in digital equipment and high-frequency equipment such as computers and others. By the way, the electromagnetic interference refers to a phenomenon in which high frequency signals circulating in such equipment are radiated from the lines of the equipment to the outside so as to interfere with the other equipment.
Conventional electromagnetic control technologies include a method that suppresses the radiation of disturbing waves by covering the lines radiating disturbing waves with electromagnetic energy absorbing materials such as a ferrite-containing rubber sheet. However, the amount of energy absorbed by such a sheet is only 2-4 dB, so that the sufficient suppression of disturbing waves has not been achieved when the radiation is strong.
Also, there are radiation suppression measures using magnetic resin compounds for circuit boards, but this method has been not practicable because of the substantially increased cost of the boards. Further, mosaic boards having the magnetic resin compounds limited only to the line portions requiring them has been manufactured in order to reduce cost, but such mosaic boards is not in practical use because the flexibility of board design is impaired remarkably.
It is therefore an object of the invention to provide a covering sheet permitting increased pbu of a signal line such as a signal bus for a computer with the smallest difference in signal waveforms and delay times on the line, a triplate line using the sheet, a signal bus for computers using the sheet, and a covering structure of electric circuits using the sheet.
Another object of the invention is to provide a covering sheet for permitting more effective prevention of electromagnetic interference, a triplate line using the sheet, a signal bus for a computer using the sheet, and a covering structure of electronic circuits using the sheet.
According to the present invention, a covering sheet includes at least one magnetic material layer made of a resin compound having an oxide magnetic material or a metal magnetic material mixed therein, a ground conductor layer laminated on one surface of the magnetic material layer, and a plurality of via holes for passing a conductor for grounding the ground conductor layer.
A target signal line or signal bus formed on a circuit board is covered with such a covering sheet, and one end of the conductor passing through via holes is connected to the ground conductor layer, and then the other end of the conducting unit is connected to a ground conductor of the circuit board, thereby a triplate line structure being constructed. This structure can increase the pbu of the signal line or signal bus. From an analysis of the mechanism of pulse transmission on lines, it is known that a leading cause of the distorting of pulse shapes is the components of higher order harmonics included in reflected negative pulses from branches and positive pulses from terminals in the signal line or signal bus. Therefore, when signals in the signal line or signal bus have the frequency components of the signals extended as near as possible to the resonance frequencies of the line, the delay time of the pulses can be reduced because the build up of pulses are made earlier and the lines can be stabilized by the suppression of resonance.
Further, such a triplate line structure can realize the absorption and shielding of unwanted signals at the same time, and thus can suppress the external radiation of unwanted signals from the signal line or signal bus, thereby permitting more effective measures against electromagnetic interference. Also, a large scale integrated circuit (LSI) and the like mounted on the circuit board are covered with the covering sheet and one end of conducting unit passing through via holes is connected to the ground conductor layer and, at the same time, the other end of the conducting unit is connected to a ground conductor of the circuit board, thereby a triplate line structure being constructed. Such a triplate line structure can suppress the external radiation of unwanted signals from this electronic circuit, thus permitting more effective measures against electromagnetic interference.
A plurality of conducting unit connected through the plurality of via holes to the ground conductor layer so as to ground the ground conductor layer are preferably provided.
Also, according to the present invention, a covering sheet includes a laminate consisting of at least one magnetic material layer made of a resin compound having an oxide magnetic material or a metal magnetic material mixed therein and at least one dielectric layer having a permittivity lower than that of the magnetic material layer, and a ground conductor layer laminated on one surface of the laminate.
A target signal line or signal bus formed on a circuit board is covered with such a covering sheet having a dielectric layer, and one end of the conducting unit passing through via holes is connected to the ground conductor layer, and, at the same time, the other end of the conducting unit is connected to a ground conductor of the circuit board, thereby a triplate line structure being constructed. This triplate line structure can increase the pbu of the signal line or signal bus and also make the characteristic impedance of the sheet-covered portion near to free space impedance, because the dielectric layer has a permittivity lower than that of the magnetic material layer, thereby permitting the suppression of changes in the characteristic impedance of the signal line or signal bus.
Further, such a triplate line structure can realize the absorption and shielding of unwanted signals at the same time, and thus can suppress the external radiation of unwanted signals from the signal line or signal bus, or electronic circuits, thereby permitting more effective measures against electromagnetic interference.
Preferably, the dielectric layer is adjacent to the ground conductor layer, or the magnetic material layer is adjacent to the ground conductor layer.
Furthermore, according to the present invention, a covering sheet includes a magnetic material layer made of a resin compound having an oxide magnetic material or a metal magnetic material mixed therein, a dielectric layer being laminated on the magnetic material layer with one surface of the dielectric layer adjacent to the magnetic material layer and having a permittivity lower than that of the magnetic material layer, and a ground conductor layer laminated on the other side of the dielectric layer.
A target signal line or signal bus formed on a circuit board is covered with such a covering sheet having the dielectric layer, and one end of the conducting unit passing through via holes is connected to the ground conductor layer, and, at the same time, the other end of the conducting unit is connected to a ground conductor of the circuit board, thereby a triplate line structure being constructed. This triplate line structure can increase the pbu of the signal line or signal bus and also make the characteristic impedance of the sheet-covered portion near to free space impedance, because the dielectric layer has a permittivity lower than that of the magnetic material layer, thereby permitting the suppression of changes in the characteristic impedance of the signal line or signal bus.
Further, such a triplate line structure can realize the absorption and shielding of unwanted signals at the same time, and thus can suppress the external radiation of unwanted signals from the signal line or signal bus, or electronic circuits, thereby permitting more effective measures against electromagnetic interference.
Preferably, the dielectric layer is a layer of solid dielectric material or mainly a layer of air.
Preferably, a plurality of via holes for passing conducting unit for grounding the ground conductor layer are further provided. In this case, a plurality of conducting unit electrically connected to the ground conductor layer through the plurality of via holes so as to ground the ground conductor layer are preferably further provided.
According to the present invention, further, a triplate line or a signal bus for a computer having a triplate line structure, includes an insulator circuit board, a micro-strip line formed on one surface of the insulator circuit board, a ground conductor formed on the other surface of the insulator circuit board, and a covering sheet having an above described structure and being applied on the micro-strip line with the ground conductor positioned outside, wherein the ground conductor is electrically connected to the ground conductor.
Also according to the present the invention, a triplate line includes an insulator circuit board, a micro-strip line formed on one surface of the insulator circuit board, a first covering sheet having the above described structure and being applied on the micro-strip line with the ground conductor positioned outside, and a second covering sheet having the above described structure and being applied on the other surface of the insulator circuit board with the ground conductor positioned outside, wherein the ground conductors of the first and second covering sheets are electrically connected to a ground conductor of the insulator circuit board.
The constructing of a signal line or signal bus in such a triplate line structure can increase the pbu of the signal line or signal bus. From an analysis of the mechanism of pulse transmission on lines, it is known that a leading cause of distorting pulse shapes is the components of higher order harmonics included in the reflected negative pulses from branches and positive pulses from terminals in signal line or signal bus. Therefore, when signals in the signal line or signal bus have the frequency components of the signals extended as near as possible to the resonance frequencies of the line, the delay time of the pulses can be reduced because the build up of pulses is made earlier and the line can be stabilized by the suppression of resonance. That is, the resonance of the bus is so enough suppressed as to lessen a reduction in terminal voltage caused by negative pulses being reflected at the branch and coming therefrom. For this reason, resonance suppression in a distributed constant manner and a reduction in pulse build up time permits more effective driving of high frequency clocks.
In addition to this, by providing the dielectric layer having a permittivity lower than that of the magnetic material layer, the characteristic impedance of the sheet-covered portion can be made near to free space impedance, thereby permitting the suppression of changes in the characteristic impedance of the signal line or signal bus.
Further, such a triplate line structure can realize the absorption and shielding of unwanted signals at the same time, and thus can suppress the external radiation of unwanted signals from the signal line or signal bus thereby permitting more effective measures against electromagnetic interference.
Further, according to the present invention, a covering structure of electronic circuits includes an insulator circuit board, an electronic circuit formed on one surface of the insulator circuit board, a ground conductor formed on the other surface of the insulator circuit board, and a covering sheet having the above described structure and being applied on the electronic circuit with the ground conductor positioned outside, wherein the ground conductor is electrically connected to the ground conductor.
Because the absorption and shielding of unwanted signals are not only problems for buses but also are important problems for general electronic equipment, lines of disturbing sources are covered with the covering sheet of the invention, and further the ground conductor layer is grounded, thereby permitting the measures against electromagnetic interference which realize the absorption and shielding of unwanted signals in general electronic equipment at the same time.
This is not limited to lines but is the same in electronic circuits such as LSI placed on a circuit board. That is, according to the invention, the covering structure of electronic circuits includes an insulator circuit board, an electronic circuit formed on one surface of the insulator circuit board, a ground conductor formed on the other surface of the insulator circuit board, and a covering sheet having the above described structure and being applied on the electronic circuits with the ground conductor positioned outside, wherein the ground conductor is electrically connected to the ground conductor. As a result, the covering structure of electronic circuits can realize the absorption and shielding of unwanted signals at the same time and therefore can suppress the external radiation of unwanted signals in the electronic circuits such as LSI, thereby permitting more effective measures against electromagnetic interference.
Preferably, the ground conductor is connected to the ground conductor at a plurality of points.
Also, preferably, the ground conductor is electrically connected to the ground conductor via a plurality of via holes passing through the sheet.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.